Nonaqueous electrolyte batteries, in which a carbon material or a lithium-titanium oxide is used as a negative electrode active material and a layered oxide including nickel, cobalt, manganese, and the like is used as a positive electrode active material, secondary batteries in particular, have already been put to practical use as a power source in a wide range of fields. Modes of such nonaqueous electrolyte batteries span over far ranges from small-sized batteries for various electronic devices to large-sized batteries for electric automobiles and the like. In an electrolyte for such secondary batteries, unlike a nickel-hydrogen battery or a lead storage battery, used is a nonaqueous organic solvent, in which ethylene carbonate, methyl ethyl carbonate, and the like are mixed. The electrolyte using such a solvent has oxidation resistance and reduction resistance that are higher than those of an aqueous electrolyte, and thus electrolysis of the solvent hardly occurs. For that reason, the nonaqueous secondary battery can realize a high electromotive force of from 2 V to 4.5 V.
On the other hand, many of the organic solvents are flammable materials, and thus the safety of the nonaqueous secondary battery is apt to be inferior to the secondary battery using an aqueous solution, in principle. Although various measures are being taken to improve the safety of the secondary battery using the electrolyte of organic solvent base, such measures are not necessarily sufficient. Furthermore, for the nonaqueous secondary battery, a dry environment is necessary in the production process, and thus the production cost is consequently increased. In addition, the electrolyte of organic solvent base has inferior electro-conductivity, and thus the internal resistance of the nonaqueous secondary battery is apt to increase. These have been big issues in applications for an electric automobile and a hybrid electric automobile in which the battery safety and the battery cost are emphasized, and in an application for a large-sized storage battery for electricity storage. In order to solve the problems of the nonaqueous secondary battery, a secondary battery using an aqueous electrolyte has been proposed. However, the active material may easily become dislodged from the current collector due to the electrolysis of the aqueous electrolyte, and hence the operation of the secondary battery is not stable, which has been problematic in performing satisfactory charge and discharge.